Method for leak testing an environmental enclosure

ABSTRACT

Methods and apparatus are disclosed for leak testing the ventilation system of an environmental enclosure using a gas that is naturally present in ambient air, such as nitrogen, oxygen, argon, or carbon dioxide, as a tracer gas. In one embodiment, a gas filter capable of filtering all of the tracer gas from the air flowing through the filter is installed in the ventilation system. Testing is performed by operating the ventilation system to cause outside air to flow through the filter and into the enclosure so as to establish positive pressurization inside the enclosure. A gas monitor placed inside the enclosure is used to detect for the presence of leaks in the ventilation system by monitoring the concentration of the tracer gas inside the enclosure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is the National Stage of InternationalApplication No. PCT/US03/33506, filed Oct. 22, 2003, which claims thebenefit of U.S. provisional application No. 60/421,593, filed Oct. 24,2002.

FIELD

The present disclosure concerns a method and apparatus for leak testingan environmental enclosure used in a polluted atmosphere, such as anoperator cab of a vehicle.

BACKGROUND

Vehicles used in polluted atmospheres, such as those used in mining oragricultural work, are equipped with air filtration equipment forprotecting the operators of such equipment from airborne contaminants.Such vehicles typically have an enclosed operator cab and a ventilationsystem having an air inflow conduit for feeding a motor-driven fan orblower. The fan induces air to flow through a dust filter and in someinstallations, an activated-charcoal filter for adsorbing harmfulvapors/gases, after which the filtered air is conveyed into the operatorcab.

Enclosed operator cabs can provide very high levels of protection fromairborne contaminants so long as clean, filtered air is introduced intothe cab with positive air pressurization of the cab interior. However,leaks in the ventilation system can allow airborne contaminants to enterthe operator cab. Typically, the areas within a ventilation system thathave a tendency to cause leaks include the sealing area around thefilter, the joints between separate portions of ductwork, and theopenings in the ductwork provided for the electrical wiring of the fans.If major leaks occur, the effectiveness of the cab filtration system canbe severely diminished, thereby compromising the safety of the operator.Thus, the ventilation system should be periodically leak tested toensure the cab enclosure provides sufficient protection for theoperator.

One method for leak testing the ventilation system of a cab enclosure isspecified in ASAE (American Society of Agricultural Engineers) StandardS525. In this method, the vehicle being tested is driven over anon-paved surface to increase the levels of aerosol and dust in theatmosphere surrounding the vehicle. As the vehicle is driven, oneoptical particle counter is used to measure ambient aerosol and dustconcentrations outside the operator cab of the vehicle and anotheroptical particle counter is used to measure aerosol and dustconcentrations inside the operator cab. For a cab to be consideredacceptable, the ratio of the concentrations outside the cab to theconcentrations inside the cab must be greater than 50. Heitbrink et al.,“Review of Ambient Aerosol Test Procedures in ASAE Standard S525,”Journal of Agricultural Safety and Health, 4(4): 255-266 (1998).

The foregoing method suffers from the drawback that the concentration ofambient aerosols varies with location and time of year. Thus, the testcan be impractical in certain locations or during certain times of theyear when the ambient aerosol concentration is not large enough toovercome any extraneous aerosol generation in the cab. Id.

In another method for leak testing the ventilation system of an operatorcab, the cab is placed inside a laboratory test chamber and exposed toan atmosphere containing a constant level of ethyl acetate. During thetest, the ventilation system of the cab is operated to cause thesurrounding atmosphere to flow through a filter capable of filteringethyl acetate and into the interior of the cab. A gas monitor placedinside the cab is used to detect for the presence of leaks in theventilation system by monitoring the concentration of ethyl acetateinside the cab. Although more reliable than the method for testing cabsin the field set forth by ASAE Standard S525, laboratory testing is muchmore inconvenient than such field-testing since the cab to be testedmust be driven or otherwise transported to a testing facility.

Accordingly, there exists a need for new and improved systems for leaktesting ventilation systems of enclosed operator cabs.

SUMMARY

According to one aspect, methods are provided for leak testing theventilation system of an environmental enclosure using a gas that isnaturally present in ambient air (e.g., nitrogen, oxygen, argon, orcarbon dioxide) as a tracer gas. An embodiment of such a method includesinducing outside air to flow through a filter in the ventilation systemand into the enclosure so as to establish positive pressurization insidethe enclosure. The filter includes filter media selected to filtertracer gas from the air stream flowing through the filter to cause adecrease in the concentration of tracer gas inside the enclosure. Duringthe test, the concentration of tracer gas inside the enclosure ismonitored to determine the lowest achievable concentration of tracerinside the enclosure.

To determine whether there are any leaks in the ventilation system, thelowest achievable concentration of tracer gas inside the enclosure iscompared to the expected concentration of tracer gas inside theenclosure due to losses through the filter. The presence of leaks in theventilation system is revealed if the lowest achievable concentration oftracer gas is greater than the expected concentration of tracer gasinside the enclosure due to losses through the filter.

Desirably, the filter is designed to be 100% efficient; that is, thefilter is capable of removing all of the tracer gas from the air flowingthrough the filter. Using such a filter, the presence of leaks isrevealed if the lowest achievable concentration of tracer gas is greaterthan zero.

In a disclosed embodiment, carbon dioxide that is naturally present inthe ambient air is used as the tracer gas for leak testing an enclosure.Hence, in this embodiment, the filter media is selected to filter carbondioxide from the air stream flowing through the filter. In particularembodiments, for example, soda lime is used as the filter media forabsorbing carbon dioxide from the air flowing through the filter.However, various other types of filter media, such as sodium hydroxide,calcium hydroxide or lithium hydroxide, also may be used.

The use of a naturally-occurring component of air as a tracer gas forleak testing an enclosure, such as described above, provides severaladvantages. In particular, vehicles can be easily tested in the field,without the need for an expensive or elaborate test chamber, since thetracer gas is naturally present in the atmosphere surrounding thevehicle to be tested. Moreover, such field-testing requires only the useof a single monitoring device, which is used for measuring theconcentration of the tracer gas inside the enclosure being tested. Incontrast, the test procedure specified by ASAE Standard S525 requires aparticle counter for monitoring particle concentrations outside theenclosure being tested and another particle counter for monitoringparticle concentrations inside the enclosure. Further, using a componentof air as the tracer gas eliminates the constraints associated withusing ambient aerosols and dust for testing an enclosure, such asspecified by ASAE Standard S525.

The foregoing and other features and advantages of the invention willbecome more apparent from the following detailed description of severalembodiments, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an enclosed operator cab of avehicle.

FIG. 2 is a perspective view of a filter, according to one embodiment,configured to fit in the ventilation system of an operator cab for thepurpose of leak testing the ventilation system.

FIG. 3 is an enlarged cross-sectional view of the filter of FIG. 2 takenalong line 3-3 in FIG. 2.

FIG. 4 is a perspective view of a filter, according to anotherembodiment, configured to fit in the ventilation system of an operatorcab for the purpose of leak testing the ventilation system.

FIG. 5 is a cross-sectional view of the filter of FIG. 4, taken along aplane perpendicular to the longitudinal axis of the filter.

DETAILED DESCRIPTION

FIG. 1 illustrates a method, according to one embodiment, for leaktesting the ventilation system 10 of an environmental enclosure, such asthe illustrated enclosed vehicle operator cab 12, using a gas that isnaturally present in ambient air (e.g., nitrogen, oxygen, argon, orcarbon dioxide) as a tracer gas. For the purpose of testing theventilation system 10, the existing filter of the vehicle is temporarilyremoved and replaced with a test filter, indicated at 16, capable offiltering the tracer gas from the air flowing through the filter 16. Thetest filter 16 desirably is 100% efficient; that is, the filter 16 iscapable of removing all of the tracer gas from the air flowing throughthe filter.

The ventilation system 10 includes ductwork 14 defining an inlet conduit20 and one or more airflow inducers 18 (e.g., fans or blowers). Theinducers 18 are operable to induce outside air to flow through the inletconduit 20 and the filter 16, and into the cab 12 through an opening 22,as indicated by arrows A.

The operator cab 12 can be the operator cab of any of various types ofequipment, such as, without limitation, industrial and agriculturalequipment, such as trucks, front-end loaders, tractors, drillingmachines, bulldozers, pan-scrapers, draglines, and excavators ormilitary vehicles, such as tanks. In addition, the methods and apparatusdisclosed herein can also be applied to various other types ofenvironmental enclosures, such as rooms or buildings equipped withfiltration equipment to prevent the ingress of outside contaminants(e.g., clean rooms used in semiconductor or pharmaceuticalmanufacturing).

The filter 16 contains filter media selected to filter the tracer gasfrom the air flowing through the filter 16. In a specific approach, forexample, carbon dioxide that is naturally present in the ambient airsurrounding the cab 12 is used as the tracer gas. Hence, in thisapproach, any of various chemical absorbents, such as soda lime, sodiumhydroxide, calcium hydroxide or lithium hydroxide, can be used as filtermedia in the filter 16 for filtering carbon dioxide from the ambientair. Further details of a filter 16 for filtering carbon dioxide fromair are described below in connection with FIGS. 2 and 3.

To determine whether there are any leaks in the ventilation system 10,the inducers 18 are activated to induce outside air to flow through theventilation system 10 and into the cab 12 to establish positivepressurization inside the cab 12. A suitable gas monitor, indicated at24, is used to monitor the concentration of the tracer gas inside thecab 12 during the test. Initially, the concentration of the tracer gasinside the cab 12 is approximately the same as the concentration of thetracer gas in the ambient air outside the cab 12. As filtered airdepleted in the tracer gas flows into the cab 12, the concentration ofthe tracer gas inside the cab 12 decreases. The test is carried outuntil the concentration of the tracer gas inside the cab 12 reaches aminimum level at or above zero. Since the filter 16 in this embodimentis 100% efficient, the concentration of the tracer gas inside the cab 12will be reduced to zero if there are no leaks in the ventilation system10. However, the presence of leaks in the ventilation system 10 isrevealed if the concentration of the tracer gas inside the cab 12 isreduced to a minimum level greater than zero.

If it is determined that there are leaks in the ventilation system 10,then further tests can be performed to identify the exact locations ofsuch leaks. In one approach, for example, leaks are identified byflowing tracer gas from a pressurized source of such tracer gas (e.g., agas cylinder filled with a charge of the tracer gas) over the externalsurface areas of the ventilation system 10 that could be contributing tothe leaks while monitoring the concentration of the tracer gas insidethe cab 12. Typically, such areas of the ventilation system 10 that havea tendency to cause leaks include the sealing area around the filter 16,the joints between separate portions of ductwork 14, and the openings inthe ductwork 14 provided for the electrical wiring of the inducers 18.If a leak exists in a specific area of the ventilation system 10, thenthere will be a sudden increase in the concentration of the tracer gasmeasured inside the cab 12 as tracer gas is flowed over that area. Oncethe leaks are identified, appropriate steps can be taken to repairand/or replace the components of the ventilation system 10 causing theleaks.

Although the filter 16 is described as having an efficiency of 100%,this is not a requirement. Accordingly, filters having efficiencies lessthan 100% also may be used to perform a leak-test on the ventilationsystem 10. In one approach, for example, the concentration of the tracergas in the ambient air outside the cab 12 is measured with the monitor24 to determine the expected concentration of tracer gas inside the cab12 due to losses through the filter. The cab 12 is then pressurized inthe manner described above to determine the lowest achievableconcentration of tracer gas inside the cab 12, which is then compared tothe expected concentration of tracer gas inside the cab due to lossesthrough the filter. The presence of leaks in the ventilation system 10is revealed if the lowest achievable concentration of tracer gas insidethe cab is greater than the expected concentration of tracer gas due tolosses through the filter.

For example, if the concentration of carbon dioxide in the atmospheresurrounding the cab 12 is 400 ppm and the filter 16 is designed toremove 98% of the carbon dioxide from air flowing through the filter,the expected concentration of carbon dioxide inside the cab 12 due tolosses through the filter is 8 ppm (0.02·400 ppm). Thus, for thisexample, the presence of leaks in the ventilation system 10 is revealedif the lowest achievable concentration of carbon dioxide inside the cab12 is greater than 8 ppm.

Referring to FIGS. 2 and 3, there is shown a test filter 16, accordingto one embodiment, configured to filter carbon dioxide from ambient airflowing through the filter. As shown, the filter 16 in the illustratedconfiguration has a generally rectangular filter housing 30, with filtermedia 38 contained within the housing 30. Air enters the filter 16 fromthe air inlet side on the back, or hidden, side of the air filter 16 asillustrated in FIG. 2. After passing through the air filter 16, filteredair depleted in carbon dioxide exists from the air outlet side 32,flowing in general in the direction of the arrows in FIGS. 2 and 3.

As best illustrated in FIG. 3, the filter 16 includes an inlet-sidefibrous electrostatic filter element 34 and an outlet-side fibrouselectrostatic filter element 36, although other types of filter elementsalso may be used. The space between the filter elements 34 and 36 ispacked with filter media 38 capable of filtering carbon dioxide from theair flowing through the filter. In particular embodiments, the filtermedia 38 is a chemical absorbent, such as soda lime, sodium hydroxide,calcium hydroxide or lithium hydroxide, for absorbing carbon dioxidefrom the air flowing through the filter 16. Filter elements 34 and 36serve to trap airborne particulate matter and retain the filter media 38within the housing 30. A gasket 40 surrounding the periphery of theoutlet side 32 serves to seal the filter 16 inside the ventilationsystem.

Since the sealing area around the periphery of the existing filter ofthe cab is a common source of leaks, the housing 30 of the test filter16 desirably has the same overall dimensions as the existing filter ofthe enclosure to be tested. Also, a gasket that is identical to theexisting gasket desirably is used with the test filter 16. In thismanner, the integrity of the gasket design and the interface areabetween the existing filter and the surrounding ductwork 14 is tested ina leak-test of the ventilation system 10. Alternatively, if desired, theexisting gasket of the ventilation system may be used with the testfilter 16.

The construction of the filter 16 is not limited to that of theillustrated embodiment. In alternative embodiments, for example, thehousing 30 of the filter 16 may be cylindrical in shape or have any ofvarious geometric shapes. In addition, reference is made to U.S. Pat.No. 5,423,903 to Schmitz et al., which discloses an activated charcoalfilter for an operator cab. The filter in the '903 patent can be adaptedto filter carbon dioxide from an air stream by replacing the activatedcharcoal with soda lime or other suitable absorbent materials.

If a component of air other than carbon dioxide is used as the tracergas to leak-test the ventilation system 10, then the filter media 38 isselected for filtering that component from the stream of air passingthrough the filter. For example, if oxygen or nitrogen is used as thetracer gas, the filter media 38 may comprise a molecular sieve selectedto adsorb either oxygen or nitrogen from the air stream passing throughthe filter.

Referring to FIGS. 4 and 5, a carbon dioxide filter according to anotherembodiment is indicated generally at 50. The filter 50 in theillustrated configuration is generally cylindrical in shape and has anouter metal screen 52, an outer or inlet side filter element 54, aninner or outlet side filter element 56, and filter media 58 (e.g., sodalime) interposed between the filter elements 54 and 56. Filter element54 in the illustrated form is a pleaded style filter element, althoughthis is not required. Air enters the filter 50 through the screen 52,flows through filter element 54, filter media 58, filter element 56, andexits the filter through an outlet 60, in the direction of the arrows inFIG. 4.

The relationship between airflow into an enclosure, such as theillustrated cab 12, and the concentration of the tracer gas inside theenclosure over a test period can be described by the vapor/gas decayequationVdx=Q _(g) dt−Qxdt,  (1)where V is the volume of the enclosure, x is the concentration of thetracer gas inside the enclosure, Q_(g) is the volumetric inflow rate oftracer gas into the enclosure, Q is the total volumetric flow rate ofair through the ventilation system (including filtered and leaked gas),and t is time. Hartman, H. L., MINE VENTILATION AND AIR CONDITIONING,1961, p. 398.

Rearranging equation 1 for integration yields:

$\begin{matrix}{{\int_{x_{o}}^{x}\frac{\mathbb{d}x}{Q_{g} - Q_{x}}} = {\frac{1}{V}\ {\int_{t_{0}}^{t}\ {{\mathbb{d}t}.}}}} & (2)\end{matrix}$Solving equation 2 yields:

$\begin{matrix}{{\ln\frac{Q_{g} - {Qx}}{Q_{g} - {Qx}_{o}}} = {- {\frac{Q\;\Delta\; t}{V}.}}} & (3)\end{matrix}$Substituting Qlc for gas leakage Q_(g) into the cab, where l is thepercent leakage of outside air around and/or through the ventilationsystem, and c is the concentration of the tracer gas outside theenclosure (in percent by volume), equation 3 becomes

$\begin{matrix}{{\ln\frac{{Qlc} - {Qx}}{{Qlc} - {Qx}_{o}}} = {- {\frac{Q\;\Delta\; t}{V}.}}} & (4)\end{matrix}$Simplifying equation 4 yields:

$\begin{matrix}{{\ln\frac{{lc} - x}{{lc} - x_{o}}} = {- {\frac{Q\;\Delta\; t}{V}.}}} & (5)\end{matrix}$Solving equation 5 for Δt produces the equation

$\begin{matrix}{{\Delta\; t} = {{- \left( {\ln\frac{{lc} - x}{{lc} - x_{o}}} \right)} \cdot {\frac{V}{Q}.}}} & (6)\end{matrix}$

Hence, the change in time Δt for a test period is a function of theinitial and final concentration of the tracer gas x_(o) and x,respectively, inside the enclosure, the volume V of the enclosure, thetotal ventilation system air quantity Q, the percentage of air leakedthrough the ventilation system l, and the concentration of tracer gas coutside the enclosure. As described below, equation 6 provides the basisfor a timed performance test for determining whether the leakage of thecab 12 meets or exceeds a specified minimum allowable leakage.

In one embodiment of such a test, for example, a gas monitor is used tomeasure the concentration of tracer gas c outside the cab 12 and theinitial concentration of tracer gas x_(o) inside the cab 12. For aspecified leakage l, and assuming a filter efficiency of 100%, the finalor minimum concentration of tracer gas x inside the cab 12 is theproduct of the leakage l and the concentration of tracer gas c outsidethe cab 12 (i.e., l·c). If the filter efficiency is less than 100%, theproduct l·c is added to the expected leakage through the filter 16(i.e., the penetration of tracer gas through the filter 16) to determinethe final or minimum concentration of tracer gas x inside the cab 12.The value for the volume V in equation 6 can be measured or obtainedfrom the manufacturer of the cab 12. The value for Q can be measuredusing a conventional air flow meter or by measuring the differentialpressure across the filter and translating the differential pressureinto the air quantity Q, as further described below. Substituting thesevalues into equation 6, the time Δt required for the concentration oftracer gas inside the cab 12 to reduce to the minimum level x for thespecified leakage l is calculated. The change in time Δt provides areference value for determining whether the actual leakage of the cab 12is equal to or less than the specified minimum leakage for the cab 12.

After calculating the time Δt, the cab 12 is tested to measure theactual time required for the concentration of tracer gas inside the cab12 to reach the minimum level x. If the measured change in time is lessthan the change in time determined mathematically, then the actualleakage of the cab 12 is less than the specified leakage l. On the otherhand, if the measured change is greater than the change in timedetermined mathematically, then the actual leakage of the cab 12 isgreater than the specified leakage l. If it is determined that theactual leakage is not acceptable, the ventilation system 10 can befurther tested to identify the portions of the ventilation system 10causing the leaks, as described above, so that those portions can berepaired and/or replaced as necessary.

In some cases, the filtered air quantity Q for a particular enclosuremay not be easily determined with a conventional air flow meter. Insteadof using an air flow meter to determine the value of Q for anyenclosure, a Δp (differential pressure) v. Q flowchart can be generatedfor a particular filter 16 for relating Δp to Q for that filter. Thus,the amount of filtered air flowing into an enclosure can be determinedby measuring the differential pressure across the filter 16 andtranslating the differential pressure measurement into a filtered airquantity measurement using the flowchart.

The methods and systems described herein can be used to test theintegrity of a seal or gasket of a filter used in a ventilation system.In one embodiment, for example, a test filter capable of filtering atracer gas is installed in the ventilation system of a test stand, and aleak test is performed by flowing outside air through the ventilationsystem and into the enclosure of the test stand. Since the ventilationsystem, other than the seal of the filter, is essentially leak-free, thepresence of tracer gas inside the enclosure indicates the gasket is notsufficiently sealing the filter. Thus, in this embodiment, a leak testperformed on the ventilation system tests the ability of the gasket toprovide a fluid-tight seal for the filter.

EXAMPLES Example 1

This example illustrates the application of a timed performance test fordetermining whether the leakage of a cab meets or exceeds a specifiedminimum allowable leakage. An enclosure having a volume (V) of 52.5 ft³and a ventilation system operable to produce an airflow rate (Q) of 25cfm is tested using carbon dioxide as the tracer gas. The carbon dioxideconcentration (c) measured outside the enclosure is 425 ppm, and theinitial carbon dioxide concentration (x_(o)) measured inside theenclosure is 394 ppm. Assuming a filter efficiency of 100%, the finalcarbon dioxide concentration (x) inside the enclosure at a leakage (l)of 2% will be 8.5 ppm.

Equation 6 is based on the natural logarithm of the concentration ratio(lc−x)/(lc−x_(o)), which ranges from negative to positive infinity.Thus, if the exact limit of the final inside cab concentration (x) isused in equation 6, the natural logarithm of the concentration ratiogoes off to negative infinity and the time (t) goes off to infinity.Accordingly, for a viable application of equation 6, the finalconcentration (x) is rounded up, such as to the nearest tenth or wholenumber. In the present example, the final carbon dioxide concentration(x), which is 8.5 ppm, is rounded up to the nearest whole number, whichis 9 ppm.

Applying equation 6, the concentration of carbon dioxide enclosureinside the enclosure should reduce to 9 ppm in 14 minutes for a 2%leakage. During testing, the concentration of carbon dioxide inside theenclosure reduced to 9 ppm in less than 14 minutes, indicating that theactual leakage of the ventilation system is less than 2%. Theventilation system in this example therefore would provide at least a50:1 protection factor for the occupant of the enclosure. On the otherhand, had the time for the concentration of carbon dioxide to reduce to9 ppm exceeded 14 minutes, or if the concentration of carbon dioxidecould not be reduced to 9 ppm, then the actual leakage would be morethan 2%.

Example 2

This example demonstrates the performance of one embodiment of a carbondioxide filter having a rectangular housing, such as shown in FIGS. 2and 3. The filter includes about 6 lbs. of soda lime Puritan BennettCorp., Pleasanton, Calif.) retained between two electrostatic filterelements. The soda lime comprises about 70% calcium hydroxide (althoughother formulations also may be used). The housing has a length L (FIG.2) measured between the side walls of the housing of about 16 inches anda height H (FIG. 2) measured between the top and bottom walls of thehousing of about 6 inches. The bed of soda lime in the filter has adepth, or thickness, measured in the direction of flow of about 2.19inches.

Table 1 below illustrates the performance of the filter for airflows ofabout 15.7 cfm and 24.8 cfm into a simulated cab test stand having aninterior cab volume of about 52.3 ft³. As shown in Table 1, the filterwas 100% efficient at 15.7 cfm and 24.8 cfm, and achieved 0 ppm ofcarbon dioxide inside the cab within 16 minutes at 15.7 cfm and within4.3 minutes at 24.8 cfm.

TABLE 1 Cab Airflow Cab Airflow 15.7 24.8 cfm cfm Time Inside Conc.Inside Conc. (min) (ppm) (ppm) 0.0 389 35 1.0 402 11 2.0 369 15 3.0 30516 4.0 242 16 5.0 224 0 6.0 183 7.0 121 8.0 75 9.0 66 10.0 52 11.0 2812.0 20 13.0 8 14.0 8 15.0 12 15.5 3 16.0 0

Example 3

This example demonstrates the performance of a carbon dioxide filterhaving a cylindrical housing, such as shown in FIGS. 4 and 5. The filterin this example has an outer diameter of about 10.75 inches and a lengthof about 7 inches, and contains about 10.3 lbs. of soda lime PuritanBennett Corp.) retained between two electrostatic filter elements. Table2 below shows the performance of this filter for an airflow of about24.8-25 cfm into the 52.3 ft³ cab test stand. As shown in Table 2, thefilter was 100% efficient and achieved 0 ppm of carbon dioxide insidethe cab within 15 minutes of operation.

TABLE 2 (Cab Airflow = 24.8-25.0 cfm) Inside Conc. Outside Time (min)(ppm) Conc. (ppm) 0.0 610 558 1.0 582 564 2.0 502 568 3.0 352 576 4.0228 580 5.0 156 586 6.0 120 593 7.0 57 601 8.0 38 610 9.0 37 606 10.0 41602 11.0 36 593 12.0 31 592 13.0 27 593 14.0 16 594 15.0 0 589

Example 4

Another example of a filter has a generally rectangular housing, such asshown in FIGS. 2 and 3, that measures about 16 inches in length andabout 6 inches in height. The filter is filled with about 5.64 lbs. ofDrägersorb® 400 soda lime (Draeger Safety, Inc. of Pittsburgh, Pa.). Thebed of soda lime has a depth measured in the direction of flow of about2.19 inches. Table 3a below illustrates the performance of the filterwhen used to filter the air flowing into the 52.3 ft³ cab test stand ata flow rate of about 24.9 cfm. As shown in Table 3a, the filter was 100%efficient at 24.9 cfm and achieved 0 ppm of carbon dioxide inside thecab within 12 minutes.

The same filter was then used to filter air flowing into the test standat a flow rate of about 40 cfm. The flow rate was reduced to about 35cfm after about 15 minutes of operation and then to about 25.4 cfm afterabout 23 minutes of operation. The performance of the filter issummarized in Table 3b, which shows that the filter was about 95%efficient at 40 cfm and 100% efficient when the air flow was reduced to25.4 cfm.

TABLE 3a (Cab airflow = 24.9 cfm) Inside Conc. Outside Time (min) (ppm)Conc. (ppm) 0.0 612 590 1.0 568 594 2.0 407 579 3.0 267 614 4.0 200 6285.0 153 629 6.0 110 627 7.0 77 631 8.0 45 631 9.0 24 630 10.0 5 631 11.01 628 12.0 0 642 13.0 0 632 14.0 0 631 15.0 0 628

TABLE 3b (Cab airflow = 40 cfm at 0 ≦ t ≦ 15; 35 cfm at 16 ≦ t ≦ 20; and25.4 cfm at 23 ≦ t ≦ 44) Inside Outside Time Conc. Conc. (min) (ppm)(ppm) 0.0 624 608 1.0 570 577 2.0 333 597 3.0 184 547 4.0 124 571 5.0 85565 6.0 66 563 7.0 46 550 8.0 40 542 9.0 32 546 10.0 28 506 11.0 21 51112.0 21 544 13.0 19 511 14.0 17 521 15.0 24 516 16.0 26 525 17.0 25 52018.0 22 513 19.0 18 538 20.0 19 514 23.0 13 533 25.0 8 542 26.0 2 52327.0 3 524 28.0 6 555 29.0 1 526 30.0 2 573 32.0 0 542 35.0 0 519 37.8 0516 39.0 0 499 40.0 3 531 44 0 505

Example 5

This example demonstrates the performance of a carbon dioxide filtercomprising a John Deere model JD60R filter housing (John Deere Co.,Moline, Ill.) packed with about 7.86 lbs. of Dragersorb® 400 soda lime.The filter was initially used to filter the air flow into a John Deeremodel 7800 tractor cab. Table 4 below shows the carbon dioxideconcentration inside and outside the cab while the cab fan was operatedat its highest speed level (which is the fourth speed level of the fan)and the second highest speed level (which is the third speed level ofthe fan). The speed of the fan was reduced from the fourth speed levelto the third speed level after 20 minutes of operation. The filterachieved 0 ppm of carbon dioxide inside the cab after about 9 minutes atthe third speed level of the fan.

TABLE 4 Inside Outside Time Conc. Conc. (min) (ppm) (ppm) 0.0 461 3341.0 384 363 2.0 306 373 3.0 209 353 4.0 159 335 5.0 106 360 6.0 71 3407.0 63 340 8.0 45 346 9.0 36 344 10.0 38 347 11.0 36 321 12.0 23 34413.0 13 340 14.0 12 339 15.0 6 329 16.0 6 326 17.0 6 334 18.0 7 335 19.011 324 20.0 15 329 21.0 45 333 22.0 69 331 23.0 77 337 24.0 59 339 25.050 334 26.0 36 311 27.0 21 320 28.0 16 324 29.0 7 330 29.1 0 338

The filter was then used to filter the air flow into the 52.3 ft³ cabtest stand. Table 5 below shows the carbon dioxide concentration insideand outside of the cab at a flow rate of 47.7 cfm. As shown the filterwas 100% efficient at 47.7 cfm and achieved 0 ppm of carbon dioxideinside the cab in about 7 minutes.

TABLE 5 (Cab airflow = 47.7 cfm) Inside Conc. Outside Time (min) (ppm)Conc. (ppm) 0.0 484 321 1.0 354 337 2.0 209 339 3.0 106 343 4.0 63 3325.0 18 329 6.0 12 321 7.0 0 308 8.0 0 309 9.0 0 318 10.0 0 308

The present invention has been shown in the described embodiments forillustrative purposes only. The present invention may be subject to manymodifications and changes without departing from the spirit or essentialcharacteristics thereof. We therefore claim as our invention all suchmodifications as come within the spirit and scope of the followingclaims.

1. A method for leak testing the ventilation system of an environmentalenclosure, the method comprising: inducing air surrounding the enclosureto flow through the ventilation system and a gas filter positioned inthe ventilation system into the enclosure to establish positive pressurein the enclosure; filtering a tracer gas from the air flowing throughthe gas filter, the tracer gas comprising a gas naturally present in theair surrounding the enclosure; determining the expected predeterminedconcentration of tracer gas inside the enclosure based upon theefficiency of the filter; measuring the lowest achievable concentrationof tracer gas inside the enclosure; and detecting for the presence ofleaks in the ventilation system by comparing the lowest achievableconcentration of tracer gas inside the enclosure to the expectedpredetermined concentration of tracer gas inside the enclosure basedupon the efficiency of the filter, wherein the presence of leaks in theventilation system is indicated if the lowest achievable concentrationof tracer gas exceeds the expected predetermined concentration of tracergas.
 2. The method of claim 1, wherein the filter is capable offiltering all of the tracer gas flowing through the filter.
 3. Themethod of claim 1, wherein: the tracer gas comprises carbon dioxide; andthe filter is capable of filtering all of the carbon dioxide from theair flowing through the filter.
 4. The method of claim 1, wherein theenclosure comprises an operator cab.
 5. The method of claim 1, whereinthe tracer gas comprises nitrogen.
 6. The method of claim 1, wherein thetracer gas comprises oxygen.
 7. The method of claim 1, wherein thetracer gas comprises argon.
 8. The method of claim 1, wherein the tracergas comprises carbon dioxide.
 9. The method of claim 8, wherein thefilter comprises a filter housing and soda lime contained in the housingfor absorbing carbon dioxide from the air flowing through the filter.10. A method for leak testing the ventilation system of an environmentalenclosure, the method comprising: inducing air surrounding the enclosureto flow through the ventilation system and a gas filter positioned inthe ventilation system into the enclosure to establish positive pressurein the enclosure so as to replace air exiting the enclosure; filtering atracer gas from the air flowing through the gas filter, the tracer gascomprising a gas naturally present in the air surrounding the enclosure;calculating the predetermined time required for the concentration of thetracer gas inside the enclosure to reduce to a predetermined level at apredetermined leakage based upon the efficiency of the filter; andmeasuring the time required for the concentration of the tracer gasinside the enclosure to reduce to the predetermined level to determineif the measured time is greater than the calculated predetermined time,which is an indication that a leak exists in the system.
 11. A methodfor leak testing a ventilation system, the method comprising: inducingair outside of an enclosure to flow through the ventilation system and agas filter positioned in the ventilation system into the enclosure so asto establish positive pressure inside the enclosure, wherein the filterfilters a tracer gas from the air flowing through the filter, the tracergas comprising a gas naturally present in the air surrounding theenclosure; measuring the concentration of tracer gas inside theenclosure; and detecting for the presence of leaks in the ventilationsystem from the concentration of the tracer gas inside the enclosure;wherein detecting for the presence of leaks in the ventilation systemcomprises determining the expected predetermined concentration of tracergas inside the enclosure based upon the efficiency of the filter; andcomparing the measured concentration of tracer gas inside the enclosureto the expected predetermined concentration of tracer gas inside theenclosure based upon the efficiency of the filter to determine whetherthere are any leaks in the ventilation system, wherein the presence ofleaks in the ventilation system is indicated if the measuredconcentration of tracer gas exceeds the expected predeterminedconcentration of tracer gas.
 12. The method of claim 11, wherein thefilter is capable of filtering all of the tracer gas flowing through thefilter.
 13. The method of claim 11, wherein: the tracer gas comprisescarbon dioxide; and the filter is capable of filtering all of the carbondioxide from the air flowing through the filter.
 14. The method of claim11, wherein the tracer gas comprises carbon dioxide.
 15. The method ofclaim 14, wherein the filter comprises soda lime for filtering carbondioxide from the air flowing through the filter.